Check Engine Light On/Off (1 Viewer)

[landtoy80]

How does the CE light work?
When the CE light is on, there is a problem.
But when it turns off, does this mean that the problem has stopped or has corrected its self?

If so when I or a dealer tries to find the problem with when the light is off will we be waisting our time?
How do you find the problem when the light is off?

 

[landtank]

i think there are stored codes for those times when the light turns off. Have the truck scanned, it should be there.

 

[offroadkid]

If the light goes off by itself, then it has had 3 good global trips, (or 3 successful ignition cycles) After 3 good global trips, starts warm-up cycles. When people bring their cars into my work for an engine light, and the light is off, we can still usually check to see what the code was because the PCM stores it. Unless the DTC is erased via a scantool, or a battery disconnect, it will still be there.

In the case that the light is no longer on, we check TSB's to see if anything applies to the symptoms described by the customer. If not, then a visual inspection could help. If still nothing is found, It is pretty difficult to duplicate the concern, and the car is returned to a cust.

For example, the last vehicle I worked on today was a '03 Ram 1500 that had a engine light no, but was off when brought in. I checked for DTC's, and found 2 stored codes for the Electronic Throttle Control. The starts since set was 10, it had 3 good global trips, and was on it's 2nd warm-up cycle. I looked at the harness to the ETC, found nothing visually. I checked TSB's and found a matching TSB for "erroneous p2106, and p2108", (I think that's what they were!) The TSB had me re-program the PCM for this fault.

 

[landtoy80]

I checked the code and it was 25 and 26 but its now only 25 but I posted it on my other post.
I just want to know if I can find the problem when the light is off or if the light needs to be on to find the problem?